1. Field of the Invention
The present invention relates to an information transmission method and apparatus for multiplexing data indicating information other than video information on a video signal, and transmitting the multiplexed data.
2. Related Background Art
A conventional system, which transmits a signal obtained by multiplexing data such as character data on a video signal, and receives and demultiplexes such signal into the video signal and data like in teletext broadcasting, is known.
However, the conventional system multiplexes modulated data on a specific interval (a portion of the vertical blanking interval) of a video signal, and the receiving side demodulates the specific interval alone to obtain data. More specifically, the modulation speed, the interval to be multiplexed, and the like of data are predetermined, and cannot be changed depending on the data volume, quality of line, and the like.
The arrangement of a video input apparatus shown in FIG. 1 will be described below as an example of a conventional information transmission system. A single-focus camera unit 100 serving as a video input unit is connected to an image processing unit 200 serving as a video processing unit. The image processing unit 200 is connected to a host unit 400 via a bus interface 208. The host unit 400 controls the image processing unit 200 and the single-focus camera unit 100 via the bus interface 208.
The arrangement of the single-focus camera unit 100 will be explained below. A system control unit 106 comprises a one-chip microcomputer having functions of a CPU, ROM, RAM, control port, communication port, and the like. The system control unit 106 controls the individual devices in the single-focus camera unit to make two-way communications with the image processing unit 200, and interprets commands as control data from the host unit 400 to execute operations requested by the host unit 400.
A lens unit 101 comprises a phototaking lens, focusing lens, and a focusing ring for manually moving the focusing lens. An iris unit 102 adjusts the amount of incident light that passes through the lens unit 101, and comprises an iris and an iris ring for manually moving the iris. An image sensing element 103 such as a CCD photoelectrically converts an image obtained via the lens unit 101 and the iris unit 102 into an electrical signal. An image sensing element driving circuit 105 such as a TG controls accumulation, reading, and resetting of the image sensing element 103 in correspondence with the number of pixels of the element 103. When the driving circuit 105 is controlled by the system control unit 106 via a control signal 110, the shutter speed can be changed. A synchronization signal generation circuit 108 such as an SSG generates video synchronization signals 112 such as a horizontal synchronization signal (HD), vertical synchronization signal (VD), video clocks, and the like on the basis of the clocks generated by the image sensing element driving circuit (TG) 105. An S/Hxc2x7AGC circuit 104 performs sampling and holding to reduce noise in charges accumulated in the image sensing element 103, and adjusts the gain of a video signal 114. The S/Hxc2x7AGC circuit 104 outputs the video signal 114. When the S/Hxc2x7AGC circuit 104 is controlled by the system control unit 106 via a control signal 111, it adjusts the gain of the video signal 114. A data multiplexing and demultiplexing unit 115 multiplexes the video signal 114 and control data from the system control unit 106, and transmits multiplexed data to the image processing unit 200. Also, the data multiplexing and demultiplexing unit 115 demultiplexes data from the image processing unit 200 and supplies the demultiplexed data to the system control unit 106. A data line and data control line 113 are used for two-way data communications between the single-focus camera unit 100 and the image processing unit 200, and are connected between the serial communication port of the system control unit 106, and the data multiplexing and demultiplexing unit 115. A connector 107 can be detached from the cable 109.
The video processing unit 200 will be described below. A system control unit 250 comprises a one-chip microcomputer having functions of a CPU, ROM, RAM, control port, communication port, and the like. The system control unit 250 performs control of the individual devices in the image processing unit 200, auto white balance control, communications with the single-focus camera unit 100, and communications with the host unit 400 via the bus interface 208. Also, the system control unit 250 interprets commands as control data from the host unit 400 and executes operations requested by the host unit 400.
A data multiplexing and demultiplexing unit 231 demultiplexes a video/data multiplexed signal 232 which multiplexes a video signal and data signal into a video signal 217 and a control data signal 222. Also, the data multiplexing and demultiplexing unit 231 multiplexes data from the system control unit 250 into a signal within the vertical synchronization interval, and transmits the signal to the single-focus camera unit 100.
An A/D conversion circuit 201 converts the video signal 217 transmitted from the single-focus camera unit 100 via the cable 109 into a digital signal 218. A signal processing circuit 202 performs processing for converting the converted digital video signal 218 into a standardized digital video signal 219. The signal processing circuit 202 generates an interrupt signal for informing the system control unit 250 of white balance data for white balance control. Upon recognizing the interrupt, the system control unit 250 reads out such information (white balance data, and the like) via a serial data line 223, and writes them in its RAM area.
An encoder circuit 204 converts the standardized digital video signal 219 into a multiplexed composite signal 221, and outputs the composite signal to a video output connector 210. An image memory 206 stores digital video signals 216 and 213 from the signal processing circuit 202 and an SRC (scan rate converter circuit) 207. A memory controller circuit 205 controls reads/writes in/from the image memory 206. The SRC 207 converts and absorbs the difference between the aspect ratios of the digital video signal 213 of the image processing unit 200 and a digital video signal 214 of the host unit 400. A switch circuit 203 selects an output signal 225 to the encoder 204 from a digital video signal 219 of the signal processing circuit 202 and the digital video signal 216 of the image memory 206, and is controlled by the system control unit 250 via a control line 224. The bus interface 208 is connected to the bus of a computer as the host unit 400. The bus interface 208 performs data communications of the digital video signal 214 and control data 226 between the host unit 400 and the image processing unit 200, and allows the host unit 400 to control the memory controller 205 and the SRC 207.
Video synchronization signals 215 of the image processing unit 200 correspond to the video synchronization signals 112 of the single-focus camera unit 100, and provide video synchronization signals to the signal processing circuit 202, the memory controller 205, and the encoder 204.
A serial data line and serial data control unit 222 are used for performing two-way data communications between the single-focus camera unit 100 and the image processing unit 200, and are connected to the serial data port of the system control unit 250.
A parallel data line and control unit 226 are used for performing two-way data communications between the host unit 400 and the image processing unit 200, and are connected to the control port of the system control unit 250.
FIG. 2 shows the transmission sequence of data 10 during the vertical blanking interval between the single-focus camera unit 100 and the image processing unit 200. A vertical synchronization interval Vhd t consists of a vertical blanking interval Vb and an effective video interval Va. Each data 10 is multiplexed on a video signal during the vertical blanking interval Vb.
When data communications are to be made between the single-focus camera unit 100 and the image processing unit 200, the length of data that can be transmitted within one vertical blanking interval Vb is limited.
In the case of FIG. 1, when the image processing unit 200 transmits control data such as command data and ACK data to the single-focus camera unit 100 within one vertical synchronization interval Vt, a maximum of 19 bytes=16 bytes (command data)+3 bytes (ACK data) must normally be transmitted. In this case, since this number of bytes is smaller than 32 bytes as the maximum number of bytes that can be transmitted within a single vertical blanking period Vb, all the data can be transmitted.
However, in the case of a zoom head which requires a large information volume to be transmitted, when vertical synchronization data generated for each synchronization interval is to be transmitted together with control data such as command data and ACK data, a maximum of 45 bytes=16 bytes (command data)+3 bytes (ACK data)+26 bytes (vertical synchronization data) must be transmitted. This number of bytes exceeds 32 bytes as the maximum number of bytes that can be transmitted within a single vertical blanking period Vb.
In this manner, when auto-focusing or automatic exposure is performed in a zoom camera unit, since the image processing unit 200 transmits data required for such control to the zoom head for each vertical blanking interval Vb, the volume of data to be transmitted increases. In the apparatus in which the density of the volume of information to be transmitted is high, data transmission cannot be completed within a single vertical blanking interval Vb.
It is an object of the present invention to provide an information transmission method and apparatus, which can solve the above-mentioned problems.
It is another object of the present invention to provide an information transmission apparatus which can realize a function of multiplexing data on a video signal in accordance with the data format used and transmitting multiplexed data, with an inexpensive, simple, and small-scale circuit arrangement.
In order to achieve the above objects, according to one embodiment of the present invention, an information transmission apparatus for multiplexing data indicating information other than video information on a video signal and transmitting the multiplexed data, comprises modulation means for forming modulated data by inputting the data and modulating the input data, and outputting the formed modulated data, multiplexing means for inputting the video signal and the modulated data output from the modulation means, multiplexing the modulated data on the input video data, and outputting the multiplexed data, and control means for controlling a modulation mode in the modulation means or a multiplexing interval of the modulated data in the multiplexing means in accordance with a type of data input to the modulation means.
It is still another object of the present invention to provide an information transmission apparatus which can efficiently transmit data together with a video signal.
In order to achieve the above object, according to one embodiment of the present invention, an information transmission apparatus for multiplexing data indicating information other than video information on a video signal and transmitting the multiplexed data, comprises transmission means for multiplexing and transmitting control data in a vertical blanking interval of the video signal in an identifiable state, and control means for controlling the transmission means to preferentially multiplex and transmit the control data when the transmission means has data to be multiplexed and transmitted in the vertical blanking interval in addition to the control data, and to multiplex and transmit the data, which cannot be multiplexed in the vertical blanking interval, during an interval other than the vertical blanking interval.
It is still another object of the present invention to provide an information transmission method which can efficiently transmit data together with a video signal.
In order to achieve the above object, according to one embodiment of the present invention, an information transmission method for multiplexing data indicating information other than video information on a video signal and transmitting the multiplexed data, comprises the transmission step of multiplexing and transmitting control data in a vertical blanking interval of the video signal in an identifiable state, and the control step of controlling a transmission operation in the transmission step to preferentially multiplex and transmit the control data when there is in the transmission step data to be multiplexed and transmitted in the vertical blanking interval in addition to the control data, and to multiplex and transmit the data, which cannot be multiplexed in the vertical blanking interval, during an interval other than the vertical blanking interval.